1. Field of Invention
The present invention relates to benzofuranone derivatives. Furthermore, the present invention relates to benzofuranone derivatives used to add into plastic for improving the antioxidant ability of the polymer.
2. Background Art
When plastic is produced and processed, high temperature thermal treatment is required. During the process, the generation of free radicals and peroxides causes the fast deterioration of the plastic and reduces its physical and mechanical properties. To maintain the physical properties of the plastic, additives such as antioxidant which can capture and quench the free radicals and peroxides are widely used for plastic processing.
Antioxidants can be categorized into 3 types according to their distinct mechanisms. The first type works by capturing and quenching carbon-centered radicals, and it is called “carbon-centered radical antioxidant”. The second type has a structure of hindered phenol which works by capturing and quenching the carbon peroxides or the free radicals of oxides, and it is called “primary antioxidant”. The representative of the third type is phosphate which works by capturing and quenching the peroxides, and it is called “secondary antioxidant”. Since carbon-centered radicals are generated at the first stage during the oxidation of plastic, quenching the radical immediately will be the most effective way to protect the desired materials.
There are a few types of carbon-centered radical antioxidants; one of them is the compound with benzofuranone structure as shown below (formula (A)). Antioxidants with this kind of structure were first developed by Sandoz in 1980s (U.S. Pat. No. 4,325,863, U.S. Pat. No. 4,338,244).

But only till the middle of 1990s did Ciba introduce the first commodity with benzofuranone structure, Irganox HP-136 (as shown below, formula (B)). This antioxidant delivers excellent effects when it combines with the primary and secondary antioxidants, especially for polyolefin plastics. But it is not thermal stable due to its small molecule.

Unfortunately, the intermediate (as shown below, formula (C)) of the process for producing HP-136 raised health concerns. The commodity was discontinued from the market afterwards.

A new antioxidant with benzofuranone structure as shown in the following formula (D) was disclosed in US 2003/0109611. However, the use of this antioxidant is limited to engineering plastics such as PBT and PU. There is no application data for polyolefin plastics.

The mechanism of benzofuranone antioxidants was first published by J. Am. Chem. Soc., 2006, vol. 128, pp 16,432-16,433. The experiment demonstrated that the active hydrogen of the furan can transfer to the sterically uncrowded position of the carbonyl group by resonance, thus such kind of molecule can quench carbon-centered radicals effectively.
The hindered phenolic primary antioxidant is currently the largest single family of antioxidants, and many derivatives are included. Among these derivatives, those with COOH group are the most popular primary antioxidants to be applied for synthesizing large molecules. Below are some examples of hindered phenolic primary antioxidants.

The combination of the primary antioxidant of hindered phenol series and a variety of secondary antioxidants has been reported and commercialized (as the formula shown below). Adding the single molecule which functionally combines the primary and secondary antioxidants outperforms adding the primary or the secondary antioxidant individually. However, no publication has revealed that carbon-centered radical antioxidant and primary antioxidant can be combined in one molecule.

According to the disclosure of prior art, the derivatives of benzofuranone may provide an excellent antioxidation ability to become a good thermal stability protector. If the benzofuranone derivatives can be functionally combined with a primary antioxidant to provide a synergistic effect in antioxidation, it will be a highly desired product in the plastic field.